Ink filling device for an ink jet print head and ink print head which can be filled therewith

ABSTRACT

An ink jet printer has an ink filling device for an ink jet print head wherein the ink jet print head can be filled with the filling device. The ink filling device has an ink reservoir and a discharge opening. The print head has an ink chamber with a feed opening for ink and can be filled when it is installed in an ink jet printer. The discharge opening is arranged in a hollow body with a variable-volume that moves ink from the ink reservoir when the volume is increased and that discharges ink via the discharge opening when the volume is decreased.

BACKGROUND OF THE INVENTION

The invention relates generally to print heads for ink jet printers. Theinvention relates more particularly to an ink jet printer having an inkjet print head which can be displaced in the direction of a line ofprint between side walls of a printer frame, and having an ink fillingdevice for filling the ink jet print head.

Ink jet print heads have a limited ink supply, which is generallysufficient for printing about 1-4 million printed characters. In thecase of ink jet printers which must be available day and night, onweekends and even during holiday periods, such as those in fax machines,for example, and in uses with a high permanent loading, such as in cashregister printers, the ink supply stored in the ink jet print head isnot sufficient.

It has therefore already been proposed, in Japanese Patent DocumentJP-A-90 29 991, to refill an ink jet print head while it is installed inan ink jet printer. For this purpose, the ink jet print head is equippedwith level detectors, which detect its minimum and maximum permissibleink level. If the level falls below the minimum, the ink jet print headis transported with its feed opening underneath an ink refilling devicewhere, with the aid of an electromagnet, a nozzle connected to an inkreservoir which is placed higher up is lowered into the feed opening andis lifted off the latter after the maximum level has been reached.

This arrangement ensures that the ink jet print head is always ready toprint. On the other hand, the amount of ink transferred into the ink jetprint head is determined by electrically controlled means and dependsonly on a level detector. If the voltage supply fails during a fillingoperation, or if the level detector fails, the ink flow from the inkreservoir cannot be interrupted.

U.S. Pat. No. 4,178,595 discloses an ink jet printer in which the inkjet print head is arranged such that it can be displaced in thedirection of a line of print between side walls of the printer frame.The feed opening is arranged on one side wall of the ink jet print head,and a discharge opening of an ink filling device is arranged on one sidewall of the printer frame, aligned coaxially with the feed opening. Inthis case, the feed opening can be connected to the discharge opening ina liquid-tight manner by displacement of the ink jet print head in thedirection of a line of print toward the discharge opening.

The discharge opening of the ink filling device is fitted to avariable-volume cylinder which, when its volume is increased, removesink from an ink reservoir and, when its volume is reduced, dischargesink through the discharge opening. The cylinder is dimensioned such thatit picks up and discharges only a small amount of ink in each case. Whenits volume is reduced, a connecting line between the cylinder and theink reservoir is closed, so that no ink can flow from the ink reservoirinto the cylinder or back from the cylinder into the ink reservoir. Thereduction in volume of the cylinder is carried out by a piston which canbe displaced with the aid of an electromagnet, the increase in volume iscarried out by a spring which pushes the piston back. The amount of inkto be transferred into the ink jet print head is determined by theperiod during which current is applied to the electromagnet.

The known ink filling device additionally needs an electromagnet andadditional outlay on control for the electromagnetic. In addition, theelectromagnet has to be of powerful design, since it has to produce theflow pressure for the ink, and has to overcome the friction of thepiston in the cylinder and the restoring force of the spring.

SUMMARY OF THE INVENTION

One object of the present invention is to provide an ink jet printerhaving an ink filling device for an ink jet print head and an ink jetprint head that can be filled therewith. Another object of the presentinvention is to provide such an ink jet printer and print head whereinonly a specific amount of ink is transferred into the ink jet print headwithout requiring additional outlay for the drive system.

In meeting these and other objects, features and advantages of thepresent invention, an ink jet printer is provided having a print headwhich can be displaced in the direction of a line of print betweensidewalls of a printer frame. The printer has an ink filling device bywhich the print head can be filled while it is installed in the ink jetprinter. The filling device has an ink reservoir and a dischargeopening. The print head has an ink chamber with a feed opening forreceiving ink. The discharge opening is fitted to a variable-volumehollow body which, when its volume it increased, removes ink from theink reservoir and, when its volume is reduced, discharges ink throughthe discharge opening. The feed opening is arranged on one sidewall ofthe print head and the discharge opening is arranged on one sidewall ofthe printer frame and is aligned coaxially with the feed opening. Thefeed opening can be connected to the discharge opening in a liquid-tightmanner by displacement of the ink jet print head in the direction of aline of print toward the discharge opening. The hollow body is arrangedon the inside of the sidewall of the printer frame. The reduction involume is performed by a further displacement of the print head towardthe sidewall beyond the point where the feed opening of the print headis connected to the discharge opening. An increase in volume is carriedout by a displacement of the print head in the opposite direction withthe existing connection between the feed opening and the dischargeopening.

The invention is based on the idea that the drive motor, which is neededin any case to displace the ink jet print head between the side walls ofthe ink jet printer along the line of print, can be used to influencethe volume of the hollow body, if the hollow body is arranged on theside wall of the printer frame. The same drive motor is used for dockingthe ink jet print head with the discharge opening. The reduction involume is then carried out by further displacement of the ink jet printhead toward the side wall, beyond the point at which the feed opening ofthe ink jet print head is connected to the discharge opening. Anincrease in volume is carried out by displacing the ink jet print headin the opposite direction. Therefore, the drive motor needed to displacethe print head along the line of print, preferably a stepping motor, canalso be used to influence the volume of the hollow body, with the effectof triple use. This means that no additional drive elements arenecessary.

The arrangement according to the invention has the advantage that only awell-metered volume of ink can pass to the ink jet print head. Withregards to the flow of ink, the arrangement has an inherently safeoperating state during every operating state of the ink jet printer.Only when the hollow body is being acted on with the effect of reducingits volume is the discharge opening opened. When the volume is constantor when the volume of the hollow body is being increased, the dischargeopening is securely closed, so that no ink can flow out.

In an advantageous development of the invention, the amount of inkdischarged from the ink filling device to the ink jet print head isdetermined by the magnitude of the adjustment or the furtherdisplacement. As a result, even ink jet print heads which have beenpartly emptied can be filled with the necessary amount of ink, and theuse of ink jet print heads having different holding capacities ispossible without changing the arrangement. The hollow body is then onlypartially emptied. As its volume is increased, its filling is also thenonly carried out in accordance with the amount of ink removed.

According to a further development of the invention, the time and/or theamount of ink of an ink fill can be controlled on the basis of aprescribable number of printed dots or printed characters that areprinted. This is because the ink jet print head was inserted into theink jet printer and, after that, the printed points or printedcharacters printed since the last ink fill. Since the ink dropletsejected by the pressure nozzles of the ink jet print head have a knownvolume, the consumption of ink can be calculated from the number ofnozzles respectively activated during printing. This applies in asimilar way to the number of printed characters, if the averageconsumption of ink for these is known. Refilling the ink jet print headwith an amount of ink corresponding to the calculated consumption thusbecomes readily possible. The time of a refilling can also be determinedin this way.

In order to permit the flushing of blocked nozzles, the reduction involume and the increase in volume can be carried out many timesimmediately one after another. This process can be triggeredautomatically by the printer control system itself by means of aspecific control command to the ink jet printer or on the basis of theoperating time of the ink jet print head.

The discharge opening is formed on a tubular connecting piece which,when the ink jet print head is displaced toward the discharge opening,penetrates into the feed opening of the ink jet print head. Built intothe connecting piece is a valve which is spring-loaded into its closedposition and which opens when the pressure in the hollow body exceeds aprescribed value. The arrangement of the connecting piece on the hollowbody has the advantage that when the displacement movement of the inkjet print head toward the discharge opening and therefore toward thehollow body is completed, the pressure in the latter immediately fallsbelow the prescribed value and the valve closes. When the ink jet printhead is displaced away from the hollow body, the connecting pieceinitially remains still connected to the feed opening, but in the areain front of the valve a negative pressure is formed, which ensures thatthe ink still remaining in this area is sucked into the ink jet printhead.

The variable-volume hollow body may optionally be constructed as acompressible balloon made of resilient plastic, as a bellows or else asa piston/cylinder arrangement.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

The invention will be explained below using an exemplary embodiment inconjunction with the appended drawings, in which

FIG. 1 illustrates a schematic front view of an ink jet printerconstructed in accordance with one embodiment of the present invention;

FIG. 2 illustrates a portion of the ink jet printer of FIG. 1 whereinthe print head is shown moved toward the discharge opening connectingthe feed opening and the discharge opening and collapsing the hollowbody; and

FIG. 3 illustrates the portion of the ink jet printer of FIG. 1 whereinthe print head is moved in the opposite direction away from thedischarge opening and prior to the hollow body increasing in volume.

FIG. 1 shows an ink jet printer, designated generally by 10, in aschematic front view. An ink jet print head 12 is guided such that itcan be displaced in both directions along a line of print on a parallelguide 18 between a left side wall 14 and a right side wall 16 of aprinter frame. The ink jet print head 12 is displaced by a beltmechanism 22 which can be driven by a stepping motor 20. The ink jetprinter 10 has a printing area P, which can be occupied at most by arecording medium. On the left in FIG. 1, the printing area P is adjoinedby an ink filling area F, in which there is an ink filling devicedesignated overall by 23.

The ink filling device 23 has a bellows 24 fastened to the inside of theleft side wall 14. The bellows is acted on, as a result of its inherentelasticity, by a restoring force acting in the direction of its maximumlongitudinal extent a. The bellows 24 can be compressed in the directionof arrow A, counter to its restoring force, parallel to the line ofprint. A connecting line 26, whose other end is connected to an inkreservoir 28, opens into the bellows 24. Built into the connecting line26 is a first valve 30, which is spring-loaded into its closed position.This valve opens when the pressure in the bellows 24 is lower by aprescribed value than the pressure in the ink reservoir 28.

Fitted perpendicular to the end face 32 of the bellows 24 facing the inkjet print head 12 is a tubular connecting piece 34, which is extended ina nozzle-like discharge opening 36. Built into the connecting piece 34is a second valve 38, which is spring-loaded into its closed position.This valve opens when the pressure in the bellows 24 exceeds aprescribed value. The discharge opening 36 is arranged to be alignedcoaxially with a feed opening 40, which is made in a side wall 42 of theink jet print head 12 facing the ink filling device 23.

The feed opening 40 can be connected to the discharge opening 36 in aliquid-tight manner by displacement of the ink jet print head 12 in thedirection of arrow A toward the discharge opening. This operating stateof the ink jet printer 10 is illustrated in FIG. 2, the bellows 24already having been compressed to a small extent with respect to itsmaximum length a. The ink in the bellows 24 is therefore under apressure which has been increased to such an extent that the first valve30 is closed and the second valve 38 is open. If the ink jet print head12 is moved further in the direction of the arrow A, the bellows 24 iscompressed to an increasing extent, and the ink flows through thedischarge opening 36 and the feed opening 40 into an ink chamber 44 inthe ink jet print head 12. As a result of the discharge of ink, thepressure in the bellows 24 decreases to such an extent that the secondvalve 38 closes.

FIG. 3 shows this operating state, the ink jet print head 12 alreadyhaving been moved away from the left side wall 14 to a small extentcounter to the direction of the arrow A. At this moment, the bellows 24begins to expand again, so that a negative pressure is produced in it.This negative pressure opens the first valve 30, so that ink can flowout of the ink reservoir 28 into the bellows 24. This operating state isillustrated in FIG. 1.

What is claimed is:
 1. An ink jet printer, comprising: an ink jet printhead which can be displaced in a direction of a line of print betweensidewalls of a printer frame, the print head having an ink chambertherein with a feed opening for receiving ink, the feed opening arrangedon a one sidewall of the print head; an ink filling device that can fillthe pint head while the printer head is installed in the ink jetprinter, wherein the filing device has an ink reservoir and a dischargeopening arranged on one sidewall of the printer frame and alignedcoaxially with the feed opening, where the feed opening can be connectedto the discharge opening in a liquid-tight manner by displacement of theprint head in the direction of a line of printer toward the dischargeopening; and a variable-volume hollow body arranged at the one sidewallof the printer frame and fitted to the discharge opening and the inkreservoir, wherein when the volume of the hollow body is increased, inkis removed from the reservoir into the hollow body and, when the volumeof the hollow body is reduced, ink from the hollow body is dischargedthrough the discharge opening and wherein volume reduction of the hollowbody is performed by a further displacement of the print head toward theone sidewall beyond a point where the feed opening of the print head isinitially connected to the discharge opening, and a volume increase isachieved by a displacement of the print head in the opposite directionwith the existing connection between the feed opening and the dischargeopening.
 2. The ink jet printer according to claim 1, wherein the amountof ink discharged from the ink filing device to the ink jet print headis determined by the magnitude of the further displacement.
 3. The inkjet printer according to claim 1, wherein a number of printed dots orprinted characters that are printed since the ink jet print head wasinserted into the ink jet printer and, after that, the printed dots orprinted characters printed since the last ink fill is registered, andthe time and/or the amount of ink of an ink fill is controlled on thebasis of a prescribable number of printed dots or printed characters. 4.The ink jet printer according to claim 1, wherein the reduction involume and the increase in volume of the hollow body can be carried outmany times immediately one after another.
 5. The ink jet printeraccording to claim 1, wherein the discharge opening is formed on atubular connecting piece which, when the ink jet print head is displacedtoward the side wall, penetrates into the feed opening of the ink jetprint head, and a valve is built into the connecting piece which isspring-loaded into its closed position and which opens when the pressurein the hollow body exceeds a prescribed value as a result of itsreduction in volume.
 6. The ink jet printer according to claim 1,wherein the variable-volume hollow body is a compressible balloon madeof resilient plastic.
 7. The ink jet printer according to claim 1,wherein the variable-volume hollow body is a bellows.
 8. The ink jetprinter according to claim 1, wherein the variable-volume hollow body isa piston and cylinder arrangement.